As the demand for producing smaller line widths of integrated circuit increases, the use of conventional photolithography process to define line widths that are smaller than the wavelength of light for implementing nano-scale features becomes increasingly difficult due to the diffraction of light. Although subnano-scale features have also been studied, they still cannot be implemented in mass production because the current commercially available manufacturing equipment is not compatible with the subnano-scale process. Therefore, a nano-imprint lithography (NIL) has been developed to meet the requirements for processing fine line widths, wherein the technology is adaptable to low-cost mass production utilizing an enlarged feature-processing area.
Nano-imprint lithography uses an imprint force to transfer nano-scale features that are previously formed on a mold onto a moldable layer applied on a substrate. The moldable layer is made of a polymer such as polymethyl methacrylate (PMMA). After the moldable layer is molded, a plurality of semiconductor processes are subsequently applied to define a device with nano-scale line widths. FIG. 3A to FIG. 3C schematically illustrate the process of nano-imprint lithography, including heating, imprinting, cooling and demolding steps. In the heating step illustrated in FIG. 3A, a moldable layer 23 applied over a substrate 21 is heated to the required operating temperature. During the imprinting step of FIG. 3B, a mold 11 with nano-scale features 13 are mounted on a first molding plate 12, and a substrate 21 is mounted on a second molding plate 26. The mold 11 moves towards the substrate 21 by means of a driving source 14. When the mold 11 comes into contact with and then presses the moldable layer on the substrate 21, the features on the mold 11 are transferred onto the moldable layer 23. After the moldable layer 23 cools down to an appropriate temperature, the moldable layer 23 is demolding from the mold 11, as shown in FIG. 3C. Thereby, the nano-imprint lithography is accomplished.
For this recently developed technology, parallelism between the mold and the substrate and uniformity of imprint force applied during imprinting are crucial to the imprinting quality. Specifically, since the mold and the substrate are respectively mounted on the first and second molding plates, the uniformity of the applied imprinting force is determined on the basis of the pressure distribution of the first and second molding plates. Therefore, if the pressure distribution on the molding plates and the parallelism between the mold and the substrate are not adequately controlled, the imprinting precision is adversely affected, and the nano-scale features on the mold or even the substrate will be damaged. Compared to conventional hot embossing, the nano-imprint lithography requires higher imprint precision, higher parallelism and uniformity of imprint pressure. The current processing apparatus does not meet the high requirements of nano-imprint lithography.
FIG. 4 shows an apparatus for molding microsystem structures disclosed in U.S. Pat. No. 5,993,189. A mold 63 having nano-scale features are mounted on an upper carrier 61, while a substrate 64 is mounted on a lower carrier 62. The lower carrier 62 moves upward under guide 65 to perform imprinting. In this apparatus, no parallelism adjustment device is provided. Therefore, the parallelism between the mold 63 and the substrate 64 is not ensured due to possible manufacturing errors or an improper assembly of components such as the mold and guide.
FIG. 5 shows of a molding apparatus disclosed in PCT patent No. WO 0169317. An imprint mold 71 and a substrate 72 are respectively connected to individual oil hydraulic cylinders 73, 74. The mold 71 comes into contact with the substrate 72 by means of the cylinder 73 to effect the imprint process. With the limited resilience of an O-ring 76 installed inside the oil hydraulic cylinder 75, the mold 71 and the substrate 72 are subject to a shift in parallelism adjustment before contacting each other. The use of the oil hydraulic cylinders 75, 77 makes the whole structure and operation complex. Furthermore, the oil hydraulic system has disadvantages such as poor control response.
FIG. 6 shows the fluid pressure imprint lithography disclosed in U.S. Pat. No. 6,482,742, which has problems similar to the above. An elastic sealing member 81 seals a mold 82 and a substrate 83 stacked together. After the stack is placed in a pressure chamber 84, a fluid is charged in the pressure chamber 84 through an inlet 85. Thus, the imprint process is achieved by the fluid pressure. Thereafter, the fluid is drained through an outlet 86 and the substrate 83 is removed. The sealing and imprinting of this apparatus are complex and time-consuming, which is unfavorable to efficient mass production. Furthermore, since the processing of the mold 82 and the substrate 83 requires stacking, sealing, transferring into the pressure chamber, and a pressure increasing and decreasing steps, it is difficult to achieve precision alignment due to the combined variability of all the processing steps.
FIG. 7 shows a molding apparatus disclosed in PCT patent WO 0142858. A pressure chamber 92 is mounted under the substrate 91. A resilient film 93 is established between the pressure chamber 92 and the substrate 91. A highly pressurized liquid is charged in the pressure chamber 92 to perform the imprint process. This method is complex and requires generating high pressure, which consumes a lot of energy and may cause environmental pollution.
Therefore, there is a need for a parallelism adjustment device suitable for nano-imprint lithography providing reduced manufacturing and assembly errors, uniformity of imprint pressure, and improved nano-imprint quality. Furthermore, the parallelism adjustment device should have a simple construction that can respond quickly and easily, and that can be manufactured and operated at low cost.